While plastic bottles with handles, particularly larger bottles of 32 ounces and larger, are widely used they have drawbacks in manufacture and in use.
With respect to plastic bottles with handles for lifting, carrying and pouring, they generally are made by the extrusion blow molding process from materials which include polyethylene and polyvinyl chloride.
In an extrusion blow-molding process an extruder initially forms large diameter preforms, hollow tubes known as parisons, and the parisons while at fusion temperatures, are positioned within blow molds having the desired final shape of the bottles. In each blow mold a portion of the parison is pinched off to form a handle shape, and the pinched parison is blown to its final bottle dimensions with a hollow handle and an interconnecting web. Thereafter, the web is removed to provide a handle for gripping, lifting, carrying and pouring.
However, the extrusion and other blow molding methods which result in bottles with hollow handles have shortcomings. In forming the hollow handles, relatively high plastic temperatures and substantial parison thickness are required to provide satisfactory fusion in the pinched and blown parison. Also the parison must have a large enough diameter so that it will essentially traverse the breadth of the bottle when pinched and blown. In addition, decreasing the amount of plastic used to form the bottles, known as "light weighting", is limited in many cases by the need for adequate parison thickness to provide the requisite fusion along the extensive pinched off areas. Another limitation is that the required large diameter parison produces bottles having wide variations in wall thicknesses, especially at and near the sidewall at the bottom juncture and at the shoulder area--the most vulnerable areas to drop impact and denting forces. This results because the pinch off distributes the parison into thick areas at each end of the pinch off and in very thin areas in the blown bottle at right angles to it.
Still another important limitation is that the relatively high fusion temperatures required to form the pinched off, hollow handles cannot be used to form handles in the newer orientation blow-molding process for forming plastic bottles. This process differs from the hollow handle, blow-molding process in that the parison is stretched and blown while at temperatures which are much lower than the fusion temperatures, generally within the 100.degree. F. range above T.sub.c (the temperature at which the plastic material passes from the glass phase to the rubber phase). This procedure is known as stretch-blow molding or orientation-blow molding.
The problem with producing plastic containers with handles using the stretch-blow processes results from the nature of the process and condition of the plastic at the time it is biaxially oriented. First, it is not possible to produce handles by the aforementioned parison pinch-off technique because the plastic temperature required for suitable molecular orientation is much too low to permit adequate fusion of the plastic. To initially form the handle at elevated temperatures and then to cool to biaxial orientation temperatures before stretching and blowing would yield unoriented handles, and substantial other portions of the container, with inferior containment and other properties. Further, the large diameter parison required for the parison pinch-off technique reduces the amount of desired biaxial orientation in all portions of the bottle.
In addition to the foregoing, specific problems arise when utilizing the injection stretch blow molding method for producing bottles with long narrow necks and substantially expanded bodies, such as those which may be used for distilled spirits and wine. These bottles typically consist of a neck finish for engaging a cap, a short transition zone, an expanded neck portion, and expanded shoulder and body portions. The transition zone provides a necessary transition from bottle nonexpanded to expanded portions and is typically less than 1/2 inch. In forming these bottles the blow up ratio for the expanded neck portion is very low when compared to the blow up ratio for the body. Consquently, provisions must be made to avoid what would otherwise result in excessively thick, heavy and, therefore, costly wall thickness in the neck portion. These provisions may include higher plastic temperatures in the preform portion which will form the bottle neck portion than those used for the more fully expanded body portions. With such provisions the rheology of the plastic is controlled so that it will stretch and thin out more in the neck areas. This, however, is an induced result and, therefore, its success depends on the degree to which such provisions can approach the ideal which will produce the desired results. These conditions in commercial practice are generally far from ideal even for so called close process control systems. Therefore, there exists a need for manufacturing methods which can produce long narrow bottle necks, such as are desired attachment sites for handles, without resulting in excessively thick, heavy and costly wall thickness.
Thus, there is a need for new and improved bottles with handles and for new and improved methods for forming such bottles and in particular a need for pouring handles using a three to four finger grip which can be located close to the bottles' centers of gravity and which can be manufactured without costly excessive weight or process procedures or controls.